The Cephalopoda are mainly characterized by the concrescence of the foot and head.
concrescence, kon-kres′ens, n. increment: a growing together of cells or other organisms.
In the embryos of higher Vertebrates it closes in the centre, the point of concrescence forming the tympanic membrane.
concrescence con·cres·cence (kən-krěs'əns)
The growing together of separate parts. Also called coalescence.